size = 20

field = [ [ 1 for i in range(0, size+1) ] for i in range(0, size+1) ]

for i in xrange(1, size+1):
	for j in xrange(1, size+1):
		field[i][j] = field[i][j-1] + field[i-1][j]

print field[size][size]


#
# recursive solution. too slow
#
#def count_path(width, height):
#	if width == 0 and height == 0:
#		return 1
#
#	count = 0
#	if width > 0: # go right
#		count += count_path(width-1, height)
#	if height > 0: # go down
#		count += count_path(width, height-1)
#	
#	return count
#
#print count_path(20, 20)